The families of five Britons being held hostage in Iraq today marked the one-year anniversary of their capture with a plea for their safe return.

The civilian contractors were kidnapped by gunmen disguised in police uniforms at the finance ministry in Baghdad.

A group calling themselves the Islamic Shia Resistance in Iraq claimed responsibility for the abduction.

One of the hostages was named as Peter Moore, an IT consultant from Lincoln who was working for the US management consultancy BearingPoint.

The others, who were employed by the Canadian security firm GardaWorld to guard Moore, have not been officially identified.

The sister of one of the men, named as Jason, pleaded for him to be released. "We miss him dearly," the woman, identified only as Lisette, told the BBC.

"Give him back, let him come home to his family. We really miss him - there's not a day, or a minute or anything that goes by without us thinking about Jason. We really want him home."

The father of a hostage named as Alec spoke of his shock at his son's capture and his belief that he would eventually be freed. He told BBC Radio 5 Live he had to "believe that the outcome's going to be positive".

"To be honest, we were so shocked by the news because, like every individual, one often thinks it will never happen to you, it will always happen to someone else," he said.

"As things develop, you sort of live with it, although you never completely get used to it. You've got to live with it, otherwise it will destroy you."

Christopher Prentice, the British ambassador to Iraq, marked the anniversary by recording a video message in English and Arabic in which he appealed for information and called for the hostages' safe return.

"The British government remains committed to working for the release of all those held, and I appeal again to those responsible to release these men in order that they may return home," he said.

The hostages have attracted less media attention than others in similar predicaments, largely because of a Foreign Office request for minimal coverage and the kidnappers' unusual request for a media blackout.

The ministry stressed that negotiations for the captives' release were continuing.

"We continue to do everything we can to secure the safe release of the hostages and remain in close contact with the families," a spokeswoman said.

The father of one of the captives was quoted as saying that more needed to be done to free his son, and the Liberal Democrat foreign affairs spokesman, Ed Davey, questioned whether the news blackout was necessary.

"I think it is valid that we ask the Foreign Office some questions," he told BBC Radio 4's Today programme. "The families think this, that they've got to justify continuing this blackout.

"Is this the right approach? Because after a year, they feel little progress has been made."

In the past year, the kidnappers have released two videos of the captives.

On December 4, a film was broadcast on the Dubai-based al-Arabiya TV station, warning that one hostage would be killed unless British troops were withdrawn from Iraq.

One of the men, who said his name was Jason, was shown in the clip, complaining that the kidnapped men felt they had been "forgotten". The threat to kill a hostage was apparently not carried out.

A second video, broadcast by al-Arabiya on February 26, showed Moore asking the prime minister, Gordon Brown, to free nine Iraqis in exchange for the release of the five men.